Materials and methods for producing tomato yellow leaf curl virus resistance in plants

ABSTRACT

The subject invention concerns materials and methods for providing genetically-engineered resistance in plants to tomato yellow leaf curl geminivirus using a truncated version of the replication associated protein (Rep) gene of TYLCV. Virus-resistant plants produced according to the present invention have horticulturally acceptable phenotypic traits. Methods of the invention comprise transforming a plant with a polynucleotide wherein when the polynucleotide is expressed in the plant, the transformed plant exhibits resistance to plant viral infections. An exemplified embodiment utilizes a polynucleotide comprising a truncated Rep gene derived from a Florida isolate of TYLCV-Is. The methods of the invention can be used to provide resistance to TYLCV infection in plants such as tomato and tobacco. The present invention also concerns transformed and transgenic plants and plant tissue that express a polynucleotide comprising a truncated Rep gene of TYLCV.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional application Ser. No. 60/289,315, filed May 7, 2002.

The subject invention was made with government support under a research project supported by the USDA Grant Nos. 99343628423, 98341356784 and 99341358478. The government has certain rights in this invention.

BACKGROUND OF THE INVENTION

Whitefly-transmitted geminiviruses have become a major limiting factor in tomato production in Florida, the Caribbean and much of Latin America. This group of viruses is currently expanding in the Western Hemisphere, and the number of characterized geminiviruses which infect tomato in this region has increased from three to more than 17 over the last 15 years (Polston and Anderson, 1997). This expansion is continuing and reports of new epidemics are appearing almost monthly. Whitefly-transmitted viruses appear alone and in mixed infections with other geminiviruses and other viruses. Whitefly-transmitted geminiviruses are reducing tomato yields in many countries, and total crop losses are not uncommon (Polston and Anderson, 1997). In Florida, tomato production has suffered significant losses (estimated at $125 million in 1990-91) due to Tomato mottle virus (ToMoV) infection, which first appeared in 1989 and to Tomato yellow leaf curl virus (TYLCV, which has caused crop failures and increases in production costs due to increases in pesticide use.

The family Geminiviridae is divided into three genera, of which the genus, Begomovirus, contains the whitefly-transmitted geminiviruses. There are two major divisions within the genus Begomovirus, those with monopartite genomes and those with bipartite genomes. The taxonomy of Begomoviruses is in a state of confusion, due to the naming of viruses based on disease symptoms before any sequence analysis has been performed. Many of these viruses cause similar symptoms in the same host, which has resulted in very different viruses having the same or related name in the literature. This is particularly true for tomato yellow leaf curl virus (TYLCV). There are eight separate and unique Begomoviruses named TYLCV. Recent suggestions to resolve this confusion have been published, though none have been adopted by all virologists, with the result that different viruses are referred to in a number of different ways. Using the scheme suggested by Fauquet and Mayo (1999), the eight viruses are identified based on the country from where the virus was first described: from China (TYLCV-Ch), from Israel (also the first one to be described) (TYLCV-Is), from Nigeria (TYLCV-Ng), from Sardinia (TYLCV-Sar), from southern Saudi Arabia (TYLCV-SSA), from Tanzania (TYLCV-Tz), from Thailand (TYLCV-Th), and from Yemen (TYLCV-Ye). Thus, while each of these viruses is named TYLCV, each of these viruses have unique sequences with less than 90% sequence homology over the genome.

The geminivirus referred to as tomato yellow leaf curl virus-Israel (TYLCV-Is), which caused extensive losses to tomato production in the Dominican Republic (reviewed by Polston and Anderson, 1997), was found in Florida in 1997 (Polston et al., 1999). TYLCV-Is infection of tomato is a serious problem in the United States Florida, Georgia, Louisiana, and Mississippi), the Caribbean (The Bahamas, Cuba, Dominican Republic, Puerto Rico, and Jamaica), Mexico, Japan, Europe, and the Mediterranean (Canary Islands, Egypt, Israel, Cyprus, Italy, Spain, Portugal and Morocco). Incidences of TYLCV-Is are increasing and economic losses have been experienced as recently as fall of 1998. TYLCV-Is virus is widespread in Florida, is likely to increase over the next few years and will become a major constraint to tomato production in Florida. Currently, there are few commercial tomato cultivars on the market with resistance to infection by TYLCV-Is. The resistance is categorized as tolerance, since infected plants show no to slight symptoms and produce yields that are relatively unaffected by infection; however, the virus can still be detected in inoculated plants and these plants can serve as sources of inoculum for susceptible cultivars and crops (Lapidot et al., 2001).

Geminiviruses are very difficult to economically manage in fresh market tomatoes, and practically impossible to manage in processing tomatoes. At this time, geminiviruses are managed primarily through the use of a single insecticide, imidacloprid (Bayer Agricultural Products, Kansas City, Mo.), to reduce the population of the whitefly vector. Tolerance to this insecticide has already been reported (Cahill et al., 1996; Williams et al., 1996). It may be only a matter of time before imidacloprid loses efficacy in the United States and other locations. The average Florida tomato grower spent approximately $250/acre for insecticides to control ToMoV in 1994 through 1997. These costs have increased significantly as U.S. growers' struggle to manage TYLCV-Is. In Caribbean countries geminiviruses have caused many small and medium size tomato growers to go out of business due the increases in costs of production and crop losses. In Israel, where imidacloprid resistance is present, TYLCV-Is is managed by pesticide use plus exclusion; tomatoes are produced in planthouses enclosed in whitefly-proof screening material or in screened tunnels in the field. The use of these methods is expensive and is often not an economically or horticulturally realistic alternative. The least expensive and most practical control of whitefly-transmitted geminiviruses is the use of resistant cultivars. At this time there are no commercially available resistant tomato cultivars for the geminiviruses native to the Western Hemisphere. As noted above, there are only two cultivars with tolerance to TYLCV-Is that are suitable for production in the U.S. This resistance is derived from wild species of Lycopersicon, probably L. peruvianum and L. pimpinellifolium.

There are a few reports suggesting that the gene encoding the Begomovirus replication associated protein (Rep) might be used for resistance to viral infection. There has been a report that a modified ToMoV Rep mutated in an NTP-binding motif was transformed into tomato plants and demonstrated to interfere with viral replication (Stout et al., 1997). Hanson et al. (1999) analyzed phenotypes of BGYMV (bean golden yellow mosaic virus) with mutations in an NTP-binding motif of the Rep gene, and demonstrated that the NTP-binding domain is required for replication. They proposed that mutations in this motif might serve in a trans-dominant negative interference scheme for pathogen-derived resistance (also known as “dominant negative mutations”). Resistance to African cassava mosaic geminivirus (ACMV) in Nicotiana benthamiana plants was developed by transformation with ACMV Rep (Hong and Stanley, 1996).

Some viral resistance has been reported using the Rep gene of the geminivirus TYLCV from Sardinia (TYLCV-Sar). However, TYLCV-Sar is a distinct virus, only distantly related to TYLCV-Is and shows significant differences in the genomic sequence (<80% homology). Noris et al (1996) found TYLCV-Sar resistance in N. benthamiana plants using the TYLCV-Sar Cl gene that encodes a protein with a truncated C-terminal (210 amino acids). However, resistance was overcome with time. Brunetti et al. (1997) transformed tomatoes with the same construct and found that high accumulation of the truncated Rep protein was required for resistance, that high accumulation resulted in a “curled” phenotype, and that the resistance did not extend to an unrelated geminivirus. Transgenic Nicotiana benthamiana plants expressing antisense RNA to the Rep gene have been observed with resistance to TYLCV-Sar infection (Bendahmane and Gronenborn, 1997). The plants transformed according to the methods of the subject invention have a normal phenotype and are expected to be high yielding as well.

The present invention overcomes the expensive, time consuming, and limited options in the traditional plant breeding programs applied to generating virus resistant tomato cultivars.

BRIEF SUMMARY OF THE INVENTION

The subject invention concerns materials and methods for providing genetically-engineered resistance to tomato yellow leaf curl geminivirus, such as TYLCV-Israel (TYLCV-Is), in plants while maintaining acceptable phenotypic characteristics of the plant. In exemplified embodiments, the subject invention provides TYLCV-Is resistance in tomato and tobacco. Specifically, resistance is provided by transforming a plant with a truncated version of the replication associated protein (Rep) gene of TYLCV. Exemplified herein is the use of a truncated Rep gene from TYLCV-Is (Florida isolate). The full length Rep gene of TYLCV-Is encodes a virus replication related protein of approximately 357 amino acids. In an exemplified embodiment, the Rep gene used in the present methods was truncated at the 3′ end, leaving 508 nucleotides (nt) at the 5′ terminus which comprised an 82 nt intergenic sequence and a 426 nt sequence that encodes a Rep protein fragment (N-terminus) of 142 amino acids. In another embodiment, a polynucleotide that is antisense to a truncated Rep gene of the present invention is used to provide resistance to infection. The present invention demonstrates the application of genetic engineering in the development of TYLCV-Is resistance in a tomato breeding line suitable for use in a hybrid for tomato production in Florida.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representation of the binary transformation vector with the truncated TYLCV Rep gene.

FIG. 2 shows the expression cassette of pKYLX71:35S2. TL, TR=left and right T-DNA borders (see An et al. for a detailed description of their origin). The multiple cloning site for pKYLX71 and pKYLX71:35S2 (the plasmids that were used) is: HindIII*-BamHI-XhoI*-PstI-SacI*-XbaI* (* indicates unique sites). The promoter in pKYLX71:35S2 is a 35S promoter modified by a duplicated “enhancer” region. Arrows indicate the direction of transcription for the expression cassette and NPTII gene. The plasmid confers tetracycline and kanemycin resistance upon E. coli and Agrobacterium tumefaciens.

FIGS. 3A-3B show the sequence of the expression cassette in PKYLX71:35S2. The region duplicated to create the 35S2 promoter is bounded by brackets and italicized (this is the first of the two repeats), and the transcription start site, multiple cloning sites and the principal 3′ end in the rbcS-E9 3′ region are set off in bold type. The expression cassette is bounded by Eco RI and Cla I sites.

FIG. 4 shows a tomato plant (in back) transformed with the truncated Rep gene showing resistance to TYLCV. Non-transformed tomato (in front) shows TYLCV disease symptoms. The test was conducted in the field at Bradenton, Fla. during the fall of 2000. All test plants were exposed to viruliferous whiteflies prior to transplanting in the field. SEQ ID NO. 8 shows the sequence of the expression cassette in PKYLX71:35S2. The region duplicated to create the 35S2 promoter is bounded by brackets and italicized (this is the first of the two repeats), and the transcription start site, multiple cloning sites and the principal 3′ end in the rbcS-E9 3′ region are set off in bold type. The expression cassette is bounded by Eco RI and Cla I sites.

FIGS. 5A-5B show a Northern blot analyses of total RNA extracted from transgenic 2/5 Rep tobacco plants and a non-transformed control. FIG. 5A, lane 1 shows a non-transformed plant; lane 2 shows non-inoculated 2/5 Rep plant; and lanes 3 and 4 show C1T1 plants inoculated with TYLCV. FIG. 5B, shows the same blot probed with 18S rRNA gene to confirm equal loading of RNA in lanes.

BRIEF DESCRIPTION OF SEQUENCES

SEQ ID NO. 1 is a oligonucleotide used for primary PCR amplification of a fragment of the Rep gene according to the present invention.

SEQ ID NO. 2 is a oligonucleotide used for primary PCR amplification of a fragment of the Rep gene according to the present invention.

SEQ ID NO. 3 shows the amino acid sequence of a truncated Rep protein according to the present invention.

SEQ ID NO. 4 shows the nucleotide sequence of a truncated TYLCV-Is Rep gene according to the present invention that encodes the amino acid sequence of SEQ ID NO. 3 and that includes an 81 nucleotide intergenic region.

SEQ ID NO. 5 shows a nucleotide sequence that is the antisense of a truncated TYLCV-Is Rep gene of SEQ ID NO. 4 according to the present invention, including the 81 nucleotide intergenic region.

SEQ ID NO. 6 shows the nucleotide sequence of a truncated TYLCV-Is (Florida isolate) Rep gene according to the present invention that encodes the amino acid sequence of SEQ ID NO. 3 and that includes an 82 nucleotide intergenic region.

SEQ ID NO. 7 shows a nucleotide sequence that is the antisense of a truncated TYLCV-Is (Florida isolate) Rep gene of SEQ ID NO. 6 according to the present invention, including the 82 nucleotide intergenic region.

SEQ ID NO. 8 shows the nucleotide sequence of the expression cassette in PKYLX71 :35S2 according to the present invention.

DETAILED DISCLOSURE OF THE INVENTION

The present invention provides a means for producing virus resistance in tomato and other crops that are susceptible to infection by TYLCV-Is (tomato yellow leaf curl virus-Israel). In exemplified embodiments, plants having resistance to TYLCV-Is were produced. The transformed and transgenic plants produced according to the present invention exhibit normal phenotypic qualities such that the plants and their produced crop are acceptable for commercial use. Development of TYLCV-Is resistance through conventional breeding has been slow (more than 10 years for traditional breeding versus 3-5 years for genetic engineered technology), usually depends upon multiple genes, and often is compromised by linkages of resistance genes to undesirable horticultural characteristics. The present invention greatly simplifies production of TYLCV-Is resistant plants and the introduction of a TYLCV-Is resistance gene into desirable tomato lines.

The subject invention concerns methods for providing resistance to infection by a tomato yellow leaf curl virus (TYLCV) in a plant or plant tissue by transforming a plant or plant tissue with a polynucleotide selected from i) a polynucleotide comprising a fragment of a TYLCV Rep gene, wherein the fragment of the Rep gene consists of all or a portion of the 5′ intergenic region of a Rep gene and about 400 to 500 nucleotides of the 5′ coding sequence of a Rep gene; ii) a polynucleotide comprising a sequence that is antisense to the fragment of the TYLCV Rep gene, and iii) a polynucleotide comprising a sequence that hybridizes under stringent conditions with the fragment of the TYLCV Rep gene or a sequence that is antisense to the fragment of the TYLCV Rep gene. Resistance to TYLCV selected from TYLCV-China, TYLCV-Israel, TYLCV-Nigeria, TYLCV-Sardinia, TYLCV-southern Saudi Arabia, TYLCV-Tanzania, TYLCV-Thailand, and TYLCV-Yemen is specifically contemplated by the subject method. Plants that can be provided with resistance to TYLCV infection include tomato, tobacco, statice, petunia, lisianthus, tomatillo, and other plants susceptible to infection by TYLCV.

In an exemplified embodiment, the subject invention provides plants having genetically-engineered resistance to TYLCV using a polynucleotide which encodes a truncated version of the replication associated (Rep) protein of TYLCV and includes a Rep intergenic region. Preferably, the truncated Rep gene is derived from TYLCV-ls or a Florida isolate of TYLCV. In one embodiment, the Rep gene of the Florida isolate of TYLCV-Is, which encodes a virus replication related protein of 357 amino acids, was truncated at the 3′ end, leaving 508 nucleotides (nt) (SEQ ID NO. 6) at the 5′ terminus which comprises 82 nucleotides of the Rep intergenic region and 426 nucleotides that encode a Rep protein fragment of 142 amino acids (SEQ ID NO. 3). The exemplified Rep gene fragment represents a small part (approximately 40%/0) of the full-length Rep gene of the virus. In another embodiment, a polynucleotide that is antisense to a truncated Rep gene of the present invention is used to provide resistance to infection. In one embodiment, the antisense polynucleotide has a sequence shown in any of SEQ ID NOS. 5 or 7. Polynucleotide sequences that hybridize with or that have 50% or more sequence identity with the truncated Rep gene sequences or antisense sequences are also contemplated within the scope of the invention. Also contemplated within the scope of the invention are fragments of a truncated Rep gene and fragments of sequences antisense to a truncated Rep gene of the present invention, including fragments of a polynucleotide having the sequence of any of SEQ ID NOS. 4-7, and fragments of the hybridizing sequences or sequences with sequence identity, so long as the fragment when expressed in a plant confers resistance to TYLCV on that plant. Methods for generating fragments of a polynucleotide sequence are well known in the art (see, for example, Wei et al., 1983).

The truncated Rep genes of the present invention can be introduced directly into plants, such as tomato, by Agrobacterium-mediated transformation or by gene transfer through conventional breeding from the transformed breeding line and, thus, can be used to protect plants from TYLCV-Is infection. Thus, the subject invention also concerns new breeding lines of plants, including tomato, with high levels of resistance to TYLCV, such as TYLCV-Is. By using new breeding lines comprising a modified Rep gene of the present invention, breeders can generate new cultivars of tomato that are resistant to virus without sacrificing other desired agronomic and horticulture features.

In a preferred embodiment of the invention, a virus-resistant transgenic plant line prepared according to the methods described herein is crossed with a transgenic plant line that is resistant to the same virus and derived from a different transformation event to produce hybrids that exhibit increased virus resistance over the parent lines. These hybrid plants are within the scope of the present invention.

Because of the high levels of resistance conferred by the methods of the present invention, application of new tomato cultivars generated from the breeding lines containing a truncated Rep gene of the present invention can greatly reduce the production loss caused by virus infection which can decrease fruit yield by up to 100%. Moreover, the use of truncated Rep gene-containing cultivars of the present invention can significantly reduce the dependence on pesticides to control whitefly that is the vector of TYLCV-Is and other geminiviruses, and consequently reduce tomato production costs and environmental contamination by pesticides. At this time, TYLCV-Is management is heavily dependent upon a single insecticide that is translocated systemically in plants. Once the whiteflies become resistant to this insecticide, management of TYLCV-Is will be nearly impossible. Therefore, application of this invention can benefit tomato growers and society as a whole by increasing productivity and reducing production costs and environment contamination.

Preferably, truncated Rep transgenes of the present invention already have markers to assist in breeding efforts (marker-assisted selection). In contrast to the results obtained by Brunetti et al. (1997), the use of Rep transgenes of the invention, to date, have not shown any adverse affects on the phenotype of virus-resistant but non-inoculated transformed plants. Resistant plants showed no evidence of virus replication 30 to 60 days after inoculation, as established by nucleic acid spot hybridization and PCR. A truncated Rep gene of the present invention can be readily moved either through transformation or through conventional breeding techniques into new horticultural backgrounds that will provide superior horticultural traits for production. In addition, use of the truncated Rep gene of the present invention in plants does not interfere with fruit size, as do the currently available resistance genes.

The subject invention also concerns polynucleotide molecules selected from i) a polynucleotide comprising a fragment of a TYLCV Rep gene, wherein the fragment of the Rep gene consists of all or a portion of the 5′ intergenic region of a Rep gene and about 400 to 500 nucleotides of the 5′ coding sequence of a Rep gene; ii) a polynucleotide comprising a sequence that is antisense to the fragment of the TYLCV Rep gene, and iii) a polynucleotide comprising a sequence that hybridizes under stringent conditions with the fragment of the TYLCV Rep gene or a sequence that is antisense to the fragment of the TYLCV Rep gene, such that when the polynucleotide is incorporated into the genome of a plant, the plant is resistant to infection by plant viruses but without negatively impacting the phenotypic characteristics of the plant. Polynucleotide sequences that hybridize with or that have 50% or more sequence identity with the truncated Rep gene sequences or antisense sequences are also contemplated within the scope of the invention. Also contemplated within the scope of the invention are fragments of a truncated Rep gene and fragments of sequences antisense to a truncated Rep gene of the present invention, including fragments of a polynucleotide having the sequence of any of SEQ ID NOS. 4-7, and fragments of the hybridizing sequences or sequences with sequence identity, so long as the fragment when expressed in a plant confers resistance to TYLCV on that plant.

In addition, because of the redundancy of the genetic code, polynucleotides of the invention can have numerous, different sequences which encode a truncated Rep polypeptide. It is well within the skill of a person trained in the art to create alternative polynucleotide sequences encoding the same, or essentially the same, truncated Rep polypeptide. These variant or alternative polynucleotide sequences are within the scope of the subject invention. As used herein, references to “essentially the same” sequence refers to sequences which encode amino acid substitutions, deletions, additions, or insertions in a truncated Rep protein which do not materially alter the ability of the polynucleotide to confer resistance to virus infection when inserted into a plant genome. Polynucleotides of the present invention encoding conservative substitutions, whereby an amino acid of one class (non-polar, uncharged polar, basic, and acidic) is replaced with another amino acid of the same class, fall within the scope of the subject invention so long as the substitution does not materially alter the ability of the present invention to provide resistance. Also contemplated within the scope of the invention are polynucleotides that are longer or shorter than the exemplified polynucleotide so long as the longer or shorter polynucleotide confers viral resistance on the plant without negatively impacting the phenotypic characteristics of the plant.

The subject invention also concerns recombinant polynucleotide vectors comprising a truncated Rep gene of the present invention which is expressible in a suitable host plant. Suitable vectors may be selected from those known in the art including plasmids, phage DNA, or combinations of plasmids and phage DNA, yeast plasmids, and derivatives and fragments. Polynucleotides of the present invention can be inserted into the multiple cloning site of a vector, such as the commercially available pUC vectors or the pGEM vectors, which allow for the excision of the polynucleotide having restriction termini adapted for insertion into any desirable plant expression or integration vector. Other plant expression vectors can also be used in the present invention. In addition, regulatory sequences such as promoters can be operatively linked to the coding sequences of polynucleotides of the present invention. For example, the 35S or 35S² promoter of cauliflower mosaic viruses (CaMV) can be used with the subject invention. Plant promoters, such as Ap3 promoter, heat shock 80 promoter, alfalfa histone H3.2 gene promoter (Kelemen et al., 2002), E8 promoter, and the like, can be used in the present invention. Other suitable promoters include octopine synthase promoter and nopaline synthase promoter. The promoter can be a constitutive, tissue-specific, or inducible promoter.

The expression vector can also, optionally, contain a selectable marker gene. In one embodiment, a marker gene provides for antibiotic or herbicide resistance when expressed. Antibiotic resistance markers include, for example, polynucleotide that when expressed provides resistance to G418, hygromycin, bleomycin, kanamycin, gentamicin and the like. Herbicide resistance markers include, for example, a polynucleotide that when expressed provides resistance to glyphosate, sulfonylurea, and the like. In one embodiment, a polynucleotide encoding the enzyme neomycin phosphotransferase type II is incorporated into an expression vector of the invention. This enzyme confers resistance to the antibiotic kanamycin. Cells transformed with a vector of the present invention containing an antibiotic or herbicide resistance marker gene can be identified by their ability to grow in the presence of the antibiotic or herbicide.

The vector can also include a 3′ non-translated termination segment operatively linked to the 3′ end of the coding sequence of the truncated Rep gene. The 3′ termination segment can provide for the addition of a polyadenylation signal to the 3′ end of mRNA. Any 3′ termination segment suitable for use in plants is within the scope of the invention.

The present invention also concerns cells infected, transformed, or transfected with a polynucleotide comprising a truncated Rep gene of the present invention. Preferably, the truncated Rep gene is derived from TYLCV-Is and comprises a nucleotide sequence coding for a polypeptide having the amino acid sequence shown in SEQ ID NO. 3. In an exemplified embodiment, the polynucleotide comprises a nucleotide sequence shown in SEQ ID NO. 6. In one embodiment, the polynucleotide is incorporated into a suitable vector, and the recombinant vector is used to transform a bacterium or other host which can then be used to introduce the polynucleotide into a plant cell. Suitable hosts that can be infected, transformed, or transfected with a polynucleotide of the invention include gram positive and gram negative bacteria such as E. coli and Bacillus subtilis. Other suitable hosts include Agrobacterium cells, insect cells, plant cells, and yeast cells. Agrobacterium containing a polynucleotide of the invention can be used to transform plant cells with the polynucleotide according to standard methods known in the art. For Agrobacterium transformation, polynucleotide vectors of the invention can also include T-DNA sequences. Polynucleotides can also be introduced into plant cells by a biolistic method (Carrer, 1995), by electroporation, by direct gene injection, and by other methods known in the art. Plants can also be transformed with polynucleotides of the present invention using marker-free transformation techniques (Zuo et al., 2002).

The subject invention also concerns transformed and transgenic plants and plant tissue, including plant seeds, that comprise a truncated Rep gene of the present invention and that exhibit resistance to infection by plant TYLCV geminivimises such as TYLCV-Is. In one embodiment, a transformed or transgenic plant of the invention comprises a polynucleotide that comprises a truncated Rep gene of the present invention. In an exemplified embodiment, the truncated Rep gene is derived from TYLCV-Is and comprises a nucleotide sequence coding for a polypeptide having the amino acid sequence shown in SEQ ID NO. 3. In an exemplified embodiment, the polynucleotide comprises a nucleotide sequence shown in SEQ ID NO. 4 or SEQ ID NO. 6. In another embodiment, the plant comprises a polynucleotide comprising an antisense sequence shown in SEQ I]D NO. 5 and SEQ ID NO. 7. Transformed and transgenic plants and plant tissue of the invention can be prepared from plants such as tomato (Lycopersicon esqulentum), tobacco (Nicotiana species), statice (Limonium sinuatum), petunia (Petunia hybrida), lisianthus (Eustoma grandiflora), tomatillo (Physalis ixocarpa), pepper, bean, and others that can be or that are susceptible to being infected by TYLCV-Is. The subject invention also concerns progeny of transgenic plants of the invention.

As used herein, the terms “nucleic acid” and “polynucleotide” refer to a deoxyribonucleotide or ribonucleotide polymer in either single- or double-stranded form, and unless otherwise limited, would encompass known analogs of natural nucleotides that can function in a similar manner as naturally-occurring nucleotides. The polynucleotide sequences include both the DNA strand sequence that is transcribed into RNA and the RNA sequence that is translated into protein. The complementary sequence of any nucleic acid or polynucleotide of the present invention is also contemplated within the scope of the invention. The polynucleotide sequences include both full-length sequences that encode the Rep protein of the invention as well as shorter sequences derived from the full-length sequences. It is understood that a particular polynucleotide sequence includes the degenerate codons of the native sequence or sequences which may be introduced to provide codon preference in a specific host cell. Allelic variations of the exemplified sequences also come within the scope of the subject invention.

Polynucleotides and proteins of the subject invention can also be defined in terms of more particular identity and/or similarity ranges with those exemplified herein. The sequence identity will typically be greater than 60%, preferably greater than 75%, more preferably greater than 80%, even more preferably greater than 90%, and can be greater than 95%. The identity and/or similarity of a sequence can be 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% as compared to a sequence exemplified herein. Unless otherwise specified, as used herein percent sequence identity and/or similarity of two sequences can be determined using the algorithm of Karlin and Altschul (1990), modified as in Karlin and Altschul (1993). Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al. (1990). BLAST searches can be performed with the NBLAST program, score=100, wordlength=12, to obtain sequences with the desired percent sequence identity. To obtain gapped alignments for comparison purposes, Gapped BLAST can be used as described in Altschul et al. (1997). When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (NBLAST and XBLAST) can be used. See NCB/NIH website.

The subject invention also contemplates those polynucleotide molecules having sequences which are sufficiently homologous with the sequences exemplified herein so as to permit hybridization with that sequence under standard stringent conditions and standard methods Maniatis, T. et al., 1982). As used herein, “stringent” conditions for hybridization refers to conditions wherein hybridization is typically carried out overnight at 20-25 C below the melting temperature (Tm) of the DNA hybrid in 6×SSPE, 5× Denhardt's solution, 0.1% SDS, 0.1 mg/ml denatured DNA. The melting temperature is described by the following formula (Beltz, G. A. et al., 1983): Tm=81.5 C+16.6 Log [Na+]+0.41(% G+C)−0.61(% formamide)−600/length of duplex in base pairs.

Washes are typically carried out as follows:

-   -   (1) Twice at room temperature for 15 minutes in 1×SSPE, 0.1% SDS         (low stringency wash).     -   (2) Once at Tm-20 C for 15 minutes in 0.2×SSPE, 0.1% SDS         (moderate stringency wash).

Thus, specifically contemplated within the scope of the invention are polynucleotide sequences that hybridize under stringent conditions with the sequence of SEQ ID NO. 4, SEQ ID NO. 5, SEQ ID NO. 6, or SEQ ID NO. 7.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

Following are examples which illustrate procedures for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.

EXAMPLE 1 Production of Transformed Tomato Plants

A polynucleotide (SEQ ID NO. 4) from a truncated Rep gene from TYLCV-Is was prepared. The truncated Rep gene was PCR-amplified from the virus using primers EH312 and EH313 and cloned using standard methods known in the art. The nucleotide sequences of primer pair EH312 and EH313 are: (SEQ ID NO.1) EH3 12: 5′ CCA AGC TTA GGC ATT AGG TGT CCA AG 3′ Hind III (SEQ ID NO.2) EH3 13: 5′ CTC TCG AGG GAT TTA CTG CCT GAA TTG 3′ Xho I

cDNA clones of the truncated Rep gene were incorporated into a multiple cloning site of the binary vector pKYLX71:35S2 containing the enhanced 35S promoter and rbcS-E9 terminator signal (see FIG. 2). The Rep gene fragment was then incorporated into the genome of tomato (Lycopersicon esculentum Mill.) by standard Agrobacterium-mediated transformation. Agrobacterium-mediated transformation of tomato was performed using standard protocols (Armitage et al., 1988; McCormick et al., 1986). Transgenic plants were screened by NPT II selection and the presence of the transgene was confirmed by PCR amplification.

EXAMPLE 2 TYLCV-Is Resistance in Tomato Plant

Seeds harvested from transformed plants were planted, and T₁ generation seedlings were inoculated with TYLCV-Is by whitefly-transmission. At harvest (12 weeks after inoculation), more than 41% of the plants in eight out of 30 T₁ lines remained free of virus symptoms, while 100% of the non-transformed control plants developed severe symptoms (Table 1). The results indicated that the exemplified truncated Rep gene of 508 nt confers high levels of resistance to TYLCV-Is (Florida isolate) in transgenic tomato plants. In addition, the phenotype of the transformed plants was normal in almost all plants.

The T₂ generation of TYLCV truncated Rep plants was exposed to viraliferous whiteflies prior to planting in the field during the fall of 2000 and spring 2001 at Bradenton, FL. The TYLCV resistance observed in the greenhouse experiments also was evident under the harsher conditions present in the field conditions (Table 2, FIG. 4).

EXAMPLE 3 TYLCV-Is Resistance in Tobacco Plant

In order to test whether the truncated TYLCV Rep gene was effective in other plants Nicotiana tabacum cv. “Xanthi” was transformed with the same vector construct (FIG. 1) as done with tomatoes. Seven lines transformed with the truncated Rep gene showed immunity to TYLCV in tobacco. This demonstrated the resistance induced by the truncated Rep gene in a different host and in independent transformation events. No resistance was found to two other begomoviruses, cabbage leaf curl virus and tomato mottle virus (ToMoV). The mechanism of resistance induced by truncated Rep gene appeared to be due to gene silencing. This was based on Northern blots of transformed tobacco that indicated a suppression of the truncated Rep gene transcripts when the TYLCV resistant plants were challenged with TYLCV.

EXAMPLE 4 Assay of Rep and C4 Constructs in Tomato

Eight constructs containing either a TYLCV Rep gene, a TYLCV-Is C4 gene (a gene which is located within the Rep gene in a different reading frame), or modified or truncated forms of the Rep gene were evaluated in plants. The T₁ generation was inoculated using whiteflies reared on TYLCV-infected tomato plants. No symptoms were observed and TYLCV-Is (by both hybridization and PCR) was not detected in plants from three of the eight constructs (apparent immunity) (Table 1). All plants had normal phenotypes. Progeny of selected T, generation plants were inoculated with TYLCV and were evaluated in the field. As expected, plants in the T₂ generation segregated for resistance (Table 2). Two types of resistance were observed in the field plants—immunity and recovery. The phenotype of all resistant plants was normal. Plants were tested three times during the growing season for TYLCV-Is.

C4 and ΔC4 Constructs. Two constructs that contained the C4 gene that begins about 220 nt into the Rep gene, either in the sense (C4) or antisense orientation (ΔC4), and did not contain the intergenic region (IR) were evaluated. These produced no resistance in the T₁ generation (Table 1).

C1 ΔC1 NC1 and NΔC1 Constructs. Constructs that contained the intergenic region and the entire Rep gene either in the sense (C1or antisense direction (ΔC1) did not produce immunity in the T₁ generation. Preliminary data suggests that this was independent of promoter (enhanced promoter: C1 and ΔC1 vs nonenhanced promoter: NC1 and NΔC1) although data on non-enhanced lines is still being collected. However, recovery was seen in the T₁ and T₂ generation plants transformed with NC1 and NΔC1, suggesting that the promoter had some effect.

2/5 TYLCV Rep and AS 2/5 TYLCV Rep Constructs. The best resistances were obtained using constructs that contained the TYLCV-Is IR and 2/5 of the TYLCV Rep gene begining with the 5′ end of the Rep in either the sense (2/5 TYLCV Rep construct; SEQ ID NO. 6) or antisense (AS 2/5 TYLCV Rep construct; SEQ ID NO. 7) orientation (see Tables 1, 2, 3, and 4). The highest frequencies of immunity were observed with the 2/5 TYLCV Rep construct. This resistance appeared to be immunity and was observed at high frequency in the T₁ through T₃ generations. Some low rates of recovery were observed in the T₂ generation but even lower rates of recovery were. observed in the T₃ generation (T₃ generation data not shown).

EXAMPLE 5 Establishing TYLCV Rep Derived Immunity

Many plants in both the T₁ and T₂ generations transformed with the 2/5 TYLCV Rep construct showed no symptoms and no viral DNA (based on nucleic acid hybridization and PCR) after inoculation with TYLCV even when plants were tested at 3 times (4, 8, and 12 weeks after inoculation) during the growing season.

Studies were conducted to determine if virus levels were too low to detect by laboratory assays. Cuttings from susceptible plants (scions) were grafted on to inoculated transformed plants in which viral DNA could not be detected. No symptoms were present and no DNA was detected in the scions 4 weeks after the graft was established. This is in contrast to the same experiments in which susceptible scions were grafted onto non-transformed inoculated plants. These scions showed symptoms within 2-3 weeks after grafting. This strongly suggests that no virus was present in the inoculated plants, and that the mechanism of resistance prevents virus replication.

EXAMPLE 6 Transformation of Tobacco

The 2/5 TYLCV Rep construct was transformed into tobacco (Nicotiana tabacum) (Freitas-Astua, J., 2001). T₁ generation plants were tested for transgene copy number, for transcript production, and for resistance to TYLCV, and to two unrelated bipartite begomoviruses: Tomato mottle virus (ToMoV), and Cabbage leaf curl virus (CabLCV). Plants were determined to be immune to TYLCV, as evidenced by the lack of detection of virus by ELISA, PCR and nucleic acid hybridization after inoculation. This resistance was independent of transgene copy number. Transcripts were produced and transcript production was significantly reduced by challenge with TYLCV (FIGS. 5A and 5B). Transformed plants were not resistant to either ToMoV or CabCLV.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. TABLE 1 Evaluation of T₁ Generation Tomato Plants Transformed with Eight Different TYLCV Gene Constructs for Resistance to Infection by TYLCV. No. Lines No. T₁ With Mean No. T₀ Gen. Gen. No. No. Lines Transgene Freq. of Freq. of Plants that Plants Lines with And Immunity Immunity Transgene Prod. Seed Evaluated¹ Tested Transgene Immunity (%) (%) 2/5 TYLCV 50 455 35 30 ² 22 7-91 45.6 Rep AS-2/5 22 263 22 17 14 8-50 17.1 TYLCV Rep ΔC4 18 197 18 12 0 0 0 C4 1 12 1  0 0 0 0 C1 2 28 2  1 0 0 0 NC1 8 95 8  0 0 0 0 NΔC1 5 67 5  0 0 0 0 TOTAL 123 1,292 106 ¹Excludes plants that died during the evaluation. ²Data in italics is not final and is still under investigation.

TABLE 2 Evaluation of T₂ Generation Tomato Plants Transformed with Different TYLCV Gene Constructs for Resistance to Infection by TYLCV. No. No. of No. Lines Mean Freq. No. Lines Mean Freq. Lines Plants with Freq. of of with Freq. of of Construct Tested Tested¹ Immunity Immunity Immunity Recovery Recovery Recovery 2/5 13  347 13  26.6-80.0 53.8 5  3.3-31.8 13.7 TYLCV Rep AS-2/5 5 135 5 10.0-55.1 22.3 4 16.6-40.0 29.2 TYLCV Rep C1ΔC1T2 2 50 2 66.9-72.2 69.6 1 13.3 13.3 ΔC4 NT C4 NT C1 NT NC1 1 22 0 — — 1 36.3 36.3 NΔC1 2 29 0 — — 2 31.8, 100 65.9 TOTAL ¹Excludes plants that died during the evaluation.

TABLE 3 Evaluation of T₂ Generation 2/5 TYLCV Rep Construct for Resistance to Infection by TYLCV. Freq. of No. Freq. of Immunity in No. Plants Immunity in Plants with Plants with Transgene % % Line No. Tested¹ Line (%) Transgene (%) Recovery Escapes²  2-5 29 75.9 18 100 0 18.0  2-9 30 80.0 23 100 0 0 21-2 44 ³ 41.0 — 21-4 30 80.0 24 100 0 0 21-8 29 55.1 12 92 0 33.3 21-10 20 39.0 — 23-2 44 27.0 — 23-5 12 31.8 5 100 0 29.0 23-7 36 32.0 — 25-4 22 57.0 — 25-5 30 40.0 12 83.3 0 6.6 25-11 28 39.2 12 58.3 0 10.7 25-15 12 27.0 — 32-6 39 40.0 — 32-12 18 29.0 — 37-6 40 40.0 — 37-11 38 78.0 — 37-12 30 33.3 13 76.9 23.0 6.6 37-13 31 52.0 — 45-10 25 80.0 19 100 0 4.0 51-4 30 26.6 10 80 20.0 0 62-5 29 48.2 13 100 0 3.4 70-12 23 82.6 13 69 0 13.0 89-5 22 27.2 5 100 0 4.5 ¹Excludes plants that died during the evaluation. ²% Escapes - plants with no virus but no transgene was detected. (These are being re-evaluated with primers 28 and 94 that bind in the transformation vector and outside the TYLCV gene.) ³Data in italics is not final and is still under investigation.

TABLE 4 Evaluation of T₂ generation plants transformed with AS-2/5 TYLCV Rep construct for Resistance to Infection by TYLCV. No. Freq. of No. Freq. of Immunity Plants Immunity Plants with in Plants with % % Line No. Tested¹ in Line (%) Transgene Transgene (%) Recovery Escapes² 66-2 30 10.0 8 12.5 37.5 0 66-7 29 55.1 15 73.3 0 0 66-11 30 20.0 18 22.2 66.6 3.3 84-1 22 18.1 8 37.5 50.0 10.0 84-8 24 8.3 6 0.0 66.6 0 ¹Excludes plants that died during the evaluation. ²% Escapes - plants with no virus but no Transgene. (These are being re-evaluated with primers 28 and 94 that bind in the transformation vector but not the TYLCV gene.) ³Data in italics is not final and is still under investigation.

References

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1. A method for providing resistance to infection by a tomato yellow leaf curl virus (TYLCV) in a plant or plant tissue, said method comprising transforming said plant or plant tissue with a polynucleotide selected from the group consisting of: i) a polynucleotide comprising a fragment of a TYLCV Rep gene, wherein said fragment of said Rep gene consists of all or a portion of the 5′ intergenic region of a Rep gene and up to about 400 to 500 nucleotides of the 5′ coding sequence of a Rep gene, or a fragment of said polynucleotide that is capable of providing resistance to infection by said TYLCV; ii) a polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said antisense polynucleotide that is capable of providing resistance to infection; and, iii) a polynucleotide comprising a sequence that hybridizes under stringent conditions with said fragment of said TYLCV Rep gene or said sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said hybridizing polynucleotide that is capable of providing resistance to infection by said TYLCV.
 2. The method according to claim 1, wherein said fragment of said TYLCV Rep gene is derived from TYLCV-Is.
 3. The method according to claim 1, wherein said fragment of said TYLCV Rep gene is derived from a Florida isolate of TYLCV-Is.
 4. The method according to claim 1, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 4, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 5. The method according to claim 1, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 6, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 6. The method according to claim 1, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 5, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 7. The method according to claim 1, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 7, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 8. The method according to claim 1, wherein said tomato yellow leaf curl virus is selected from the group consisting of TYLCV-China, TYLCV-Israel, TYLCV-Nigeria, TYLCV-Sardinia, TYLCV-southern Saudi Arabia, TYLCV-Tanzania, TYLCV-Thailand, and TYLCV-Yemen.
 9. The method according to claim 8, wherein said tomato yellow leaf curl virus is TYLCV-Israel.
 10. The method according to claim 1, wherein said plant or plant tissue is selected from the group consisting of tomato, tobacco, statice, petunia, lisianthus, and tomatillo.
 11. The method according to claim 10, wherein said plant or plant tissue is tomato.
 12. The method according to claim 10, wherein said plant or plant tissue is tobacco.
 13. The method according to claim 1, wherein said plant or plant tissue is transformed with said polynucleotide by agroinfection, biolistic targeting, electroporation, or direct gene injection.
 14. The method according to claim 1, wherein said polynucleotide comprises regulatory sequences operably linked to said Rep gene sequence.
 15. The method according to claim 14, wherein said regulatory sequences comprise a promoter.
 16. The method according to claim 15, wherein said promoter is selected from the group consisting of constitutive promoter, tissue-specific promoter, and inducible promoter.
 17. The method according to claim 15, wherein said promoter is selected from the group consisting of CaMV 35S promoter, CaMV 35S² promoter, octopine synthase promoter, nopaline synthase promoter, Ap3 promoter, heat shock 80 promoter, alfalfa histone H3.2 gene promoter, and E8 promoter.
 18. The method according to claim 1, wherein said polynucleotide comprises a selectable marker gene.
 19. The method according to claim 18, wherein said selectable marker gene provides for antibiotic resistance when expressed.
 20. The method according to claim 19, wherein said antibiotic resistance is selected from the group consisting of resistance to G418, hygromycin, bleomycin, kanamycin, and gentamicin.
 21. The method according to claim 1, wherein said polynucleotide comprises a 3′ non-translated termination sequence.
 22. A transgenic or transformed plant or plant tissue having increased resistance to infection by a tomato yellow leaf curl virus (TYLCV), wherein said plant or plant tissue comprises a polynucleotide selected from the group consisting of: i) a polynucleotide comprising a fragment of a TYLCV Rep gene, wherein said fragment of said Rep gene consists of all or a portion of the 5′ intergenic region of a Rep gene and up to about 400 to 500 nucleotides of the 5′ coding sequence of a Rep gene, or a fragment of said polynucleotide that is capable of providing resistance to infection by said TYLCV; ii) a polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said antisense polynucleotide that is capable of providing resistance to infection by said TYLCV; and, iii) a polynucleotide comprising a sequence that hybridizes under stringent conditions with said fragment of said TYLCV Rep gene or said sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said hybridizing polynucleotide that is capable of providing resistance to infection by said TYLCV.
 23. The plant or plant tissue according to claim 22, wherein said fragment of said TYLCV Rep gene is derived from TYLCV-Is.
 24. The plant or plant tissue according to claim 22, wherein said fragment of said TYLCV Rep gene is derived from a Florida isolate of TYLCV-Is.
 25. The plant or plant tissue according to claim 22, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 4, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 26. The plant or plant tissue according to claim 22, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 6, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 27. The plant or plant tissue according to claim 22, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 5, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 28. The plant or plant tissue according to claim 22, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 7, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 29. The plant or plant tissue according to claim 22, wherein said tomato yellow leaf curl virus is selected from the group consisting of TYLCV-China, TYLCV-Israel, TYLCV-Nigeria, TYLCV-Sardinia, TYLCV-southem Saudi Arabia, TYLCV-Tanzania, TYLCV-Thailand, and TYLCV-Yemen.
 30. The plant or plant tissue according to claim 29, wherein said tomato yellow leaf curl virus is TYLCV-Israel.
 31. The plant or plant tissue according to claim 22, wherein said plant or plant tissue is selected from the group consisting of tomato, tobacco, statice, petunia, lisianthus, and tomatillo.
 32. The methed-plant or plant tissue according to claim 31, wherein said plant or plant tissue is tomato.
 33. The plant orplant tissue according to claim 31, wherein said plant or plant tissue is tobacco.
 34. The plant or plant tissue according to claim 22, wherein said plant or plant tissue is transformed with said polynucleotide by agroinfection, biolistic targeting, electroporation, or direct gene injection.
 35. The plant or plant tissue according to claim 22, wherein said polynucleotide comprises regulatory sequences operably linked to said Rep gene sequence.
 36. The plant or plant tissue according to claim 35, wherein said regulatory sequences comprise a promoter.
 37. The plant or plant tissue according to claim 36, wherein said promoter is selected from the group consisting of constitutive promoter, tissue-specific promoter, and inducible promoter.
 38. The plant or plant tissue according to claim 36, wherein said promoter is selected from the group consisting of CaMV 35S promoter, CaMV 35S² promoter, octopine synthase promoter, nopaline synthase promoter, Ap3 promoter, heat shock 80 promoter, alfalfa histone H3.2 gene promoter, and E8 promoter.
 39. The plant or plant tissue according to claim 22, wherein said polynucleotide comprises a selectable marker gene.
 40. The plant or plant tissue according to claim 39, wherein said selectable marker gene provides for antibiotic resistance when expressed.
 41. The plant or plant tissue according to claim 40, wherein said antibiotic resistance is selected from the group consisting of resistance to G418, hygromycin, bleomycin, kanamycin, gentamicin.
 42. The plant or plant tissue according to claim 22, wherein said polynucleotide comprises a 3′ non-translated termination sequence.
 43. A progeny of the plant or plant tissue of claim
 22. 44. A polynucleotide selected from the group consisting of: i) a polynucleotide comprising a fragment of a TYLCV Rep gene, wherein said fragment of said Rep gene consists of all or a portion of the 5′ intergenic region of a Rep gene and up to about 400 to 5 00 nucleotides of the 5′ coding sequence of a Rep gene, or a fragment of said polynucleotide that is capable of providing resistance to infection by said TYLCV; ii) a polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said antisense polynucleotide that is capable of providing resistance to infection by said TYLCV; and, iii) a polynucleotide comprising a sequence that hybridizes under stringent conditions with said fragment of said TYLCV Rep gene or said sequence that is antisense to said fragment of said TYLCV Rep gene, or a fragment of said hybridizing polynucleotide that is capable of providing resistance to infection by said TYLCV.
 45. The polynucleotide according to claim 44, wherein said fragment of said TYLCV Rep gene is derived from TYLCV-Is.
 46. The polynucleotide according to claim 44, wherein said fragment of said TYLCV Rep gene is derived from a Florida isolate of TYLCV-Is.
 47. The polynucleotide according to claim 44, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 4, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 48. The polynucleotide according to claim 44, wherein said polynucleotide comprising a fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 6, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 49. The polynucleotide according to claim 44, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 5, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 50. The polynucleotide according to claim 44, wherein said polynucleotide comprising a sequence that is antisense to said fragment of said TYLCV Rep gene has the nucleotide sequence shown in SEQ ID NO. 7, or a fragment of said nucleotide sequence that is capable of providing resistance to infection.
 51. The polynucleotide according to claim 44, wherein said tomato yellow leaf curl virus is selected from the group consisting of TYLCV-China, TYLCV-Israel, TYLCV-Nigeria, TYLCV-Sardinia, TYLCV-southem Saudi Arabia, TYLCV-Tanzania, TYLCV-Thailand, and TYLCV-Yemen.
 52. The polynucleotide according to claim 51, wherein said tomato yellow leaf curl virus is TYLCV-Israel. 53-56. (canceled)
 57. The polynucleotide according to claim 44, wherein said polynucleotide comprises regulatory sequences operably linked to said Rep gene sequence.
 58. The polynucleotide according to claim 57, wherein said regulatory sequences comprise a promoter.
 59. The polynucleotide according to claim 58, wherein said promoter is selected from the group consisting of constitutive promoter, tissue-specific promoter, and inducible promoter.
 60. The polynucleotide according to claim 58, wherein said promoter is selected from the group consisting of CaMV 35S promoter, CaMV 35S² promoter, octopine synthase promoter, nopaline synthase promoter, Ap3 promoter, heat shock 80 promoter, alfalfa histone H3.2 gene promoter, and E8 promoter.
 61. The polynucleotide according to claim 44, wherein said polynucleotide comprises a selectable marker gene.
 62. The polynucleotide according to claim 61, wherein said selectable marker gene provides for antibiotic resistance when expressed.
 63. The polynucleotide according to claim 62, wherein said antibiotic resistance is selected from the group consisting of resistance to G418, hygromycin, bleomycin, kanamycin, and gentamicin.
 64. The polynucleotide according to claim 44, wherein said polynucleotide comprises a 3′ non-translated termination sequence.
 65. An expression vector comprising a polynucleotide of claim
 44. 66. The expression vector according to claim 65, wherein said expression vector is suitable for expressing said polynucleotide in a plant.
 67. A plant cell comprising in its genome a polynucleotide of claim
 44. 68. A plant seed comprising in its genome a polynucleotide of claim
 44. 